Susceptibility of the breast to carcinogenesis is influenced by the developmentally dynamic state of the mammary microenvironment during the time of exposure to carcinogenic insult. For example, exposure of rats to chemical carcinogens during peripuberty, a "developmental window" of rapid mammary remodeling, is associated with increased tumorigenesis. Similar to peripuberty, post-lactational involution has been recently recognized as a developmental window of mammary gland remodeling. Although parity in general induces a long-term protective effect on life-long breast cancer risk, the mammary gland remodeling of post-lactational involution has recently been identified as contributing to the significantly increased breast cancer risk seen in post-partum women. The premise of this grant is that the brief window of post-lactational involution is a sensitive target for dietary intervention by both positive and negative agents which act as defined modifiers of human breast cancer risk. Ethanol exposure is one dietary factor which has been clearly shown to increase breast cancer risk in women in a dose-dependent fashion. However, the effects of ethanol exposure during brief periods of rapid mammary gland remodeling, such as post-lactational involution, on breast cancer risk may present unrecognized targets for dietary intervention. The purpose of this proposal is to test the hypothesis that ethanol consumption synergistically interacts with the exposure window of involution to substantially increase parity-associated breast cancer risk, and that this occurs through long-lasting effects on mammary gland structure and composition. This hypothesis will be tested in two Specific Aims, both utilizing the transgenic MMTV-Her-2/neu mice, which overexpress wild type Her2 receptors in the mammary epithelium and develop mammary tumors with a high penetrance in a parity-dependent fashion. Aim 1 will compare the ability of ethanol, fed for 14 days throughout involution, to alter the histological structure and biochemical and molecular composition of the mouse mammary gland at day 4, day 9 and day 21 of involution. These time points were chosen to compare ethanol's effects on the mammary gland at times of peak involution (day 4), newly completed remodeling (day 9) and the fully established post-lactational resting, regressed state (day 21). Aim 2 will assess the ability of the same regimen of 14 days of ethanol feeding to influence the latency, multiplicity, growth and metastasis of mammary tumors that arise spontaneously in this transgenic mouse model in a parity-dependent fashion. Tumors will be harvested and examined for effects of ethanol feeding on histopathology, blood vessel density, and biochemical expression of protein targets, and gene expression by microarray analysis. The results of these studies will establish a new paradigm for rationally designed, developmentally-targeted chemopreventive strategies to harness specific time points of physiologic mammary gland remodeling for the development of safe and effective short-term dietary interventions to prevent human breast cancer. PUBLIC HEALTH RELEVANCE: Despite the recent confirmation of ethanol as a risk factor for breast cancer, there is a need for more specific dietary recommendations that address periods of increased susceptibility of the breast of ethanol exposure, rather than total abstention. The purpose of the current research proposal is to test the hypothesis that the time period of post-lactational involution represents a potentially modifiable period of tissue reprogramming, during which time the dietary environment has the potential to enhance the long-term risk of developing parity- associated breast cancer, or alternately, protect against these insults. Using the MMTV-Her-2/Neu transgenic mouse model, in which wild type Her-2/neu is overexpressed in the mammary gland epithelium in a parity- dependent manner, we will examine how ethanol exposure during post-lactational involution alters susceptibility to parity-associated breast cancer.